The present invention is directed to a power delivery system. More particularly, the present invention is directed to a power delivery system across a wide range of frequencies.
Integrated circuits are typically assembled into packages that are mounted to a printed circuit board. The printed circuit board may be incorporated into an electronic subassembly that may be plugged into a motherboard or printed circuit board.
It is generally desirable to have a semiconductor package that is more efficient and has a high decoupling capacitance and low inductance. The effective inductance can be lowered by connecting a decoupling capacitor near to a circuit (i.e., the effective inductance is lower by reducing the lead length). Inductance is a function of path length, therefore the longer the current path, the higher the inductance. High inductance, which yields higher supply noise in semiconductor packages, reduces the performance of integrated circuits (ICs). Also, inductance between an IC and a power supply can induce spurious voltage spikes in the power supply system, which can in turn cause timing problems in signal switching.
Decoupling capacitors may be housed on semiconductor packages in order to lower the inductance through the package by reducing the lead length. Decoupling capacitors placed close to power consuming circuits may smooth out voltage variations with a stored charge on the decoupling capacitor. The stored charge may dissipate or be used as a local power supply to device inputs, thereby allowing the decoupling capacitor to negate the effects of voltage noise induced into the system by parasitic inductance. However, off-chip decoupling capacitors may not be sufficient for very high-speed microprocessor and switching I/O applications. Since the decoupling capacitors are located a relatively long distance from the circuits, the time delay caused by the long inductance path may make the off-chip capacitors unusable with gigahertz switching circuits.
In order to sustain high frequency circuit operation, an ample amount of capacitive decoupling may be provided close to the circuits. Although it is possible to integrate chip capacitors within the chip""s circuit elements, the capacitors compete for valuable die area that could be used for building additional circuits. Due to the limited area in which to build these capacitors, the overall capacitive decoupling that they provide may also be limited.
Many circuits place time varying current loads on their respective power delivery systems with various frequency components. For example, an I/O (input/output) buffer that drives a square wave requires a power delivery network capable of supplying all frequencies with low impedance. It is desirable to build a power delivery system for supplying power to integrated circuits which has the attribute of low impedance across a wide range of frequencies.